Disc drives are used for data storage in modern electronic products ranging from digital cameras to computers and network systems. Typically, a disc drive includes a mechanical portion, or head disc assembly (HDA), and electronics in the form of a printed circuit board assembly (PCB), mounted to an outer surface of the HDA. The PCB controls HDA functions and provides a communication interface between the disc drive and a host being serviced by the disc drive.
Typically, an HDA includes a magnetic disc surface affixed to a spindle motor assembly for rotation at a constant speed and an actuator assembly positionably controlled by a closed loop servo system. The actuator assembly supports a read/write head that traverses generally concentric magnetic tracks radially spaced across the disc surfaces.
Continued demand for disc drives with ever-increasing levels of data storage capacity, faster data throughput and decreasing price per megabyte have led disc drive manufacturers to seek ways to increase the storage capacity and improve overall operating efficiencies of the disc drive. Present generation disc drives typically achieve bit densities of multiple gigabits per square centimeter, Gbits/cm2. Increasing bit densities can be achieved by increasing the number of bits stored along each track, or bits per inch (BPI), generally requiring improvements in the read/write channel electronics, and/or by increasing the number of tracks per unit width, or tracks per inch (TPI), generally requiring improvements in servo control systems. As bit density increases it is not uncommon for fly heights to decrease, which heighten the need to control environmental conditions internal to the disc drive.
One approach taken by disc drive manufacturers to improve control of the internal environment has been the inclusion of pre-formed gasket material sandwiched between enclosure components. The inclusion of gasket material between a mating line of the enclosure sections precludes passage of external environmental conditions into the disc drive. For example, gaskets have been utilized to alleviate air leaks between base and top cover disc drive configurations, or between sections of clamshell style disc drive configurations. U.S. Pat. No. 4,896,231 issued to Hoppe exemplifies one such construction of a pre-formed gasket recently proposed in the art, which seals the inner workings of the disc drive from its external environment. The Hoppe solution incorporates a multi-layer approach that includes a central stiffener member sandwiched between a pair of foam layers. Typically, pre-formed gaskets, either single or multi layered, are punched from sheets of gasket material. Punched gaskets provide highly functional gaskets but result in producing large volumes of waste material as a consequence of the punching process. Additionally, as configurations change between product lines, multiple configurations of gaskets must be managed through the purchase, transport, receipt, quality conformation, stocking, and issue of the gaskets as part of the overall manufacturing process. These material management costs can easily overshadow the cost of the gasket itself.
An alternate approach is exemplified by U.S. Pat. No. 5,326,611 issued to Kishita et al, which proposes the use of a fluorosilicone rubber composition injected on a surface of one of either enclosure components of the disc drive. In addition to the use of fluorosilicone rubber, other known approaches in the art incorporate the use of formed-in-place silicone rubber gaskets. In either case, the method of application of the gasket material involves utilization of a pressurized delivery system for delivery of the material to the selected enclosure component. The delivery method is similar to (with exceptions) dispensing the gasket material through the use of a syringe. Additionally, a characteristic common to both materials is their propensity to out-gas volatiles that remain within the material subsequent to the cure process. Out-gassing, even at a significantly reduced rate, directly impact head-disc interface, leading to a deterioration in fly height and head crashes.
As such, challenges remain and a need persists for improved materials and techniques for providing gaskets that are cost effective and maintain the internal environment of a disc drive.